New utility method tpd.Underscore

A typed `_'. This is needed in a few places.

Author: odersky

src/dotty/tools/dotc/ast/tpd.scala

@@ -418,6 +418,9 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
     Thicket(valdef, clsdef)
   }
 
+  /** A `_' with given type */
+  def Underscore(tp: Type)(implicit ctx: Context) = untpd.Ident(nme.WILDCARD).withType(tp)
+
   def defaultValue(tpe: Types.Type)(implicit ctx: Context) = {
     val tpw = tpe.widen
 

src/dotty/tools/dotc/transform/ExpandSAMs.scala

@@ -74,7 +74,7 @@ class ExpandSAMs extends MiniPhaseTransform { thisTransformer =>
         val defaultSym = ctx.newSymbol(isDefinedAtFn, nme.WILDCARD, Synthetic, selector.tpe.widen)
         val defaultCase =
           CaseDef(
-            Bind(defaultSym, untpd.Ident(nme.WILDCARD).withType(selector.tpe.widen)),
+            Bind(defaultSym, Underscore(selector.tpe.widen)),
             EmptyTree,
             Literal(Constant(false)))
         cpy.Match(applyRhs)(paramRef, cases.map(translateCase) :+ defaultCase)

src/dotty/tools/dotc/transform/LazyVals.scala

@@ -278,7 +278,7 @@ class LazyVals extends MiniPhaseTransform with IdentityDenotTransformer {
         CaseDef(computedState, EmptyTree, body)
       }
 
-      val default = CaseDef(untpd.Ident(nme.WILDCARD).withType(defn.LongType), EmptyTree, Literal(Constant(())))
+      val default = CaseDef(Underscore(defn.LongType), EmptyTree, Literal(Constant(())))
 
       val cases = Match(stateMask.appliedTo(ref(flagSymbol), Literal(Constant(ord))),
         List(compute, waitFirst, waitSecond, computed, default)) //todo: annotate with @switch

src/dotty/tools/dotc/transform/PatternMatcher.scala

@@ -60,7 +60,7 @@ class PatternMatcher extends MiniPhaseTransform with DenotTransformer {thisTrans
     val sel = Ident(selector.termRef).withPos(tree.pos)
     val rethrow = tpd.CaseDef(EmptyTree, EmptyTree, Throw(ref(selector)))
     val newCases = tpd.CaseDef(
-      Bind(selector,untpd.Ident(nme.WILDCARD).withPos(tree.pos).withType(selector.info)),
+      Bind(selector, Underscore(selector.info).withPos(tree.pos)),
       EmptyTree,
       transformMatch(tpd.Match(sel, tree.cases ::: rethrow :: Nil)))
     cpy.Try(tree)(tree.expr, newCases :: Nil, tree.finalizer)

src/dotty/tools/dotc/transform/SyntheticMethods.scala

@@ -105,8 +105,7 @@ class SyntheticMethods(thisTransformer: DenotTransformer) {
      */
     def equalsBody(that: Tree)(implicit ctx: Context): Tree = {
       val thatAsClazz = ctx.newSymbol(ctx.owner, nme.x_0, Synthetic, clazzType, coord = ctx.owner.pos) // x$0
-      def wildcardAscription(tp: Type) =
-        Typed(untpd.Ident(nme.WILDCARD).withType(tp), TypeTree(tp))
+      def wildcardAscription(tp: Type) = Typed(Underscore(tp), TypeTree(tp))
       val pattern = Bind(thatAsClazz, wildcardAscription(clazzType)) // x$0 @ (_: C)
       val comparisons = accessors map (accessor =>
         This(clazz).select(accessor).select(defn.Any_==).appliedTo(ref(thatAsClazz).select(accessor)))